// FastCharStream.java
package org.apache.lucene.queryParser;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.*;

/**
 * An efficient implementation of JavaCC's CharStream interface.
 * <p>
 * Note that this does not do line-number counting, but instead keeps track of
 * the character position of the token in the input, as required by Lucene's
 * {@link org.apache.lucene.analysis.Token} API.
 */
public final class FastCharStream implements CharStream {
	char[] buffer = null;

	int bufferLength = 0; // end of valid chars
	int bufferPosition = 0; // next char to read

	int tokenStart = 0; // offset in buffer
	int bufferStart = 0; // position in file of buffer

	Reader input; // source of chars

	/** Constructs from a Reader. */
	public FastCharStream(Reader r) {
		input = r;
	}

	public final char readChar() throws IOException {
		if (bufferPosition >= bufferLength)
			refill();
		return buffer[bufferPosition++];
	}

	private final void refill() throws IOException {
		int newPosition = bufferLength - tokenStart;

		if (tokenStart == 0) { // token won't fit in buffer
			if (buffer == null) { // first time: alloc buffer
				buffer = new char[2048];
			} else if (bufferLength == buffer.length) { // grow buffer
				char[] newBuffer = new char[buffer.length * 2];
				System.arraycopy(buffer, 0, newBuffer, 0, bufferLength);
				buffer = newBuffer;
			}
		} else { // shift token to front
			System.arraycopy(buffer, tokenStart, buffer, 0, newPosition);
		}

		bufferLength = newPosition; // update state
		bufferPosition = newPosition;
		bufferStart += tokenStart;
		tokenStart = 0;

		int charsRead = // fill space in buffer
		input.read(buffer, newPosition, buffer.length - newPosition);
		if (charsRead == -1)
			throw new IOException("read past eof");
		else
			bufferLength += charsRead;
	}

	public final char BeginToken() throws IOException {
		tokenStart = bufferPosition;
		return readChar();
	}

	public final void backup(int amount) {
		bufferPosition -= amount;
	}

	public final String GetImage() {
		return new String(buffer, tokenStart, bufferPosition - tokenStart);
	}

	public final char[] GetSuffix(int len) {
		char[] value = new char[len];
		System.arraycopy(buffer, bufferPosition - len, value, 0, len);
		return value;
	}

	public final void Done() {
		try {
			input.close();
		} catch (IOException e) {
			System.err.println("Caught: " + e + "; ignoring.");
		}
	}

	public final int getColumn() {
		return bufferStart + bufferPosition;
	}

	public final int getLine() {
		return 1;
	}

	public final int getEndColumn() {
		return bufferStart + bufferPosition;
	}

	public final int getEndLine() {
		return 1;
	}

	public final int getBeginColumn() {
		return bufferStart + tokenStart;
	}

	public final int getBeginLine() {
		return 1;
	}
}
